This invention relates to a method and apparatus for buffing spherical parts and more particularly to a method and apparatus for buffing the spherical or ball portions of ball joint studs of the type utilized in motor vehicle steering systems.
Ball joint studs form a critical part of motor vehicle steering systems and must be manufactured inexpensively but with great precision. In the manufacture of ball joint studs the parts are typically cold headed from steel stock, machined to form the ball and shank portions of the stud, threaded to form a threaded portion on the lower end of the shank portion, case hardened by carburizing, oil quenched, tempered and then subjected to a finishing step in which the oxides produced on the surface of the ball during the tempering step are removed to restore the required precise polished final finish.
The final finishing step to remove the oxides on the surface of the ball has been performed, for example, in a hand buffing operation utilizing handheld buffing machines, or in a vibratory tumbling operation in which the parts are placed in a container containing abrasive material to remove the oxides in response to tumbling movement of the container.
The hand buffing procedure is unsatisfactory since it is imprecise and since it is labor intensive, thereby adding considerably to the cost of the final ball joint stud.
The vibratory tumbling procedure is unsatisfactory since it often damages the previously formed threads on the shank portion of the stud, requiring rethreading after the tumbling operation, and since it creates toxic waste disposal problems associated with the periodic replacement of the abrasive material.